Method of switching and switching device for solid state power controller applications

ABSTRACT

A solid state switching device (SSSD) for AC and DC high power solid state power controller includes, for DC applications, a MOSFET and an IGBT connected in parallel and an optional zener diode connecting a collector and a gate of the IGBT. For AC applications, the SSSD includes a “back to back” pair of MOSFETs connected in parallel with a pair of counter-parallel IGBTs, each in series with a diode, and, optionally, zener diodes “back to back” with conventional diodes connecting a collector and a gate of each of the IGBT. A method of switching establishes a sequence of turning on/off the MOSFET(s) and the IGBT(s) wherein the IGBT(s) turn on before and turn off after the MOSFET(s). A negative feedback prevents a voltage of SSSD rising above predetermined level.

BACKGROUND OF THE INVENTION

The present invention generally relates to solid state power controllertechnology and, more specifically, to devices and methods of switchingin high power AC/DC solid state power controllers.

Solid State Power Controller (SSPC) technology is gaining acceptance asa modern alternative to the combination of conventionalelectromechanical relays and circuit breakers for commercial aircraftpower distribution due to its high reliability, “soft” switchingcharacteristics, fast response time, and ability to facilitate advancedload management and other aircraft functions.

While SSPCs with current rating under 15 A have been widely utilized inaircraft secondary distribution systems, power dissipation, voltagedrop, and leakage current associated with solid state power switchingdevices pose challenges for using SSPCs in high voltage applications ofaircraft primary distribution systems with higher current ratings.

A typical SSPC generally comprises a solid state switching device(SSSD), which performs the primary power on/off switching, and aprocessing engine, which is responsible for SSSD on/off control and afeeder wire protection.

Existing aircraft applications employ exclusively a metal oxidesemiconductor field effect transistor (MOSFET) as a basic solid statecomponent for building up the SSSD. It features easy control,bi-directional conduction characteristic, and resistive conductionnature with positive temperature coefficient. To increase the currentcarrying capability and reduce the voltage drop or power dissipation,the SSSD comprises multiple MOSFETs generally connected in parallel.However, this set up does not warrant an increased capability to handlehigher fault current. During SSSD turn-off transients, generally,neither all the MOSFETs turn off simultaneously nor the fault currentdistributes evenly among the MOSFETs in such a short time. As a result,fault current capability of single MOSFET has to be considered as theworst case scenario in the design of SSSDs. Meanwhile, the resistanceand, therefore, power dissipation of the MOSFET turned on increasesignificantly with its voltage ratings. That increase greatly limits theMOSFET potential applications in the high voltage environments, such as115VAC, 230VAC, 270VDC, and 540VDC, etc., in the aircraft.

Similar to the MOSFET in gate controls, an insulated gate bipolartransistor (IGBT) features high current carrying capability, lowconduction loss at high current, availability of high voltage ratings,etc. However, a greater than 1.7V voltage associated with IGBT on-stateis still considered too high and would introduce errors at the voltagezero crossing detection. Furthermore, the limited reverse blockingcapability makes use of the conventional IGBT difficult for ACapplications and a diode would have to be added, further impacting theon state voltage. A newly developed reverse blocking IGBT (RB-IGBT) isdesigned for bi-directional power switching. But the inherent “deadband” associated with a greater than 2V on-state voltage of RB-IGBTresults in noticeable distortions in the controlled current that arehighly undesirable, if not unacceptable to existing AerospaceElectromagnetic Interference and Power Quality requirements, for powerdistribution applications.

As can be seen, there is a need for to provide a practical solution forthe solid state power switch to be used in high power AC/DC SSPCs(either with higher current ratings, e.g. >15 A, or in higher voltageapplications, e.g. ≧115VAC), particularly using existing commerciallyavailable semiconductors. There is also a need to provide such asolution, which will result in reduced power dissipation, improvedreliability and fault current handling capability, and no currentdistortions.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a method of switching a solidstate switching device having at least one metal oxide semiconductorfield effect transistor and at least one insulated gate bipolartransistor connected in parallel comprises the steps of connecting ondemand a power input to a power output through the insulated gatebipolar transistor; delaying for the dissipation of inrush current ofthe insulated gate bipolar transistor; connecting the power input to thepower output through the metal oxide semiconductor field effecttransistor; disconnecting on demand the power input from the poweroutput through the metal oxide semiconductor field effect transistor;delaying for switching off of the metal oxide semiconductor field effecttransistor; and disconnecting the power input from the power outputthrough the insulated gate bipolar transistor.

In another aspect of the present invention, a method of switching asolid state switching device having at least one metal oxidesemiconductor field effect transistor and at least one insulated gatebipolar transistor connected in parallel comprises the steps ofconnecting on demand the power input to the power output through theinsulated gate bipolar transistor; delaying for the dissipation ofinrush current of the insulated gate bipolar transistor; connecting thepower input to the power output through the metal oxide semiconductorfield effect transistor; conveying negative feedback from the poweroutput to the insulated gate bipolar transistor; disconnecting on demandthe power input from the power output through the metal oxidesemiconductor field effect transistor; delaying for switching off of themetal oxide semiconductor field effect transistor; and disconnecting thepower input from the power output through the insulated gate bipolartransistor.

In a further aspect of the present invention, a solid state switchingdevide comprises a first metal oxide semiconductor field effecttransistor; a first insulated gate bipolar transistor connected inparallel with the metal oxide semiconductor field effect transistor; andwherein the first metal oxide semiconductor field effect transistorturns on with a first predetermined delay after the first insulated gatebipolar transistor turns on and the first insulated gate bipolartransistor turns off with a second predetermined delay after the firstmetal oxide semiconductor field effect transistor turns off.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdrawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A depicts a conceptual schematic of a first embodiment of an SSSDfor AC application according to present invention;

FIG. 1B depicts a conceptual schematic of another embodiment of an SSSDfor AC application according to the present invention;

FIG. 2 depicts a conceptual schematic of embodiment of an SSSD for DCapplication according to the present invention;

FIG. 3 depicts a switching sequence according to a method of the presentinvention; and

FIG. 4 depicts a flow chart according to a method of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplatedmodes of carrying out the invention. The description is not to be takenin a limiting sense, but is made merely for the purpose of illustratingthe general principles of the invention, since the scope of theinvention is best defined by the appended claims.

Various inventive features are described below that can each be usedindependently of one another or in combination with other features.However, any single inventive feature may not address any of theproblems discussed above or may only address one of the problemsdiscussed above. Further, one or more of the problems discussed abovemay not be fully addressed by any of the features described below.

The present invention, in its various embodiments, discloses an improvedsolid state switching device and a method of switching for high powerAC/DC SSPCs either with current ratings higher than 15 A, or voltageapplications higher than 28V, particularly, for high voltageapplications of aircraft primary distribution systems.

The SSSD of present invention may improve reliability and fault currenthandling by relying on an IGBT based switch to handle switchingtransients and breaking up the fault current because a single IGBTtypically has much higher current rating than a single MOSFET in similarsize. The IGBT based switch may also provide over voltage protection forthe SSSD during heavy inductive load switching off, fault currentbreaking up transients, and lightning transients. The SSSD of presentinvention may achieve high current ratings in SSPC applications forlower than 1.7V voltage drop by connecting in parallel additionalMOSFETs without the limits of the fault current handling capability of asingle MOSFET.

Referring to FIG. 1A, in one embodiment, a schematic conceptuallyrepresents an AC SSSD 10 which may include two types of solid statebi-directional switches 11 and 12 connected in parallel. For clearerillustration of the main concept, the schematic omits gate resistors anda current sensing mechanism well known in the art.

The solid state bi-directional switch 11 may include first and secondMOSFETs 13 and 14 connected in a “back to back” fashion with a commongate 15, a common source 16 and drains 17 and 18. Multiple parallelpairs (one shown) 31 of MOSFETs may be added to the MOSFETs 13 and 14for improved current carrying capability and voltage drop.

By external (on demand) on/off commands, a drive signal of the gate 15may control the operation of the solid state bi-directional switch 11.The multiple pairs 31 of MOSFETs may act synchronously with the MOSFETs13 and 14 thereby multiplying power-carrying capability of the switch11.

The solid state bi-directional switch 12 may include first and secondconventional IGBTs 23 and 24 with gates 25, 26 and emitters 27, 28respectively and zener diodes 19 and 20. The zener diode 19 may beconnected across the collector 33 of the IGBT 24 and the gate 26 as afeedback circuit for the IGBT 24 and, respectively, the zener diode 20may be connected across the collector 32 of the IGBT 23 and the gate 25as a feedback circuit for the IGBT 23. The zener diodes 19 and 20 may beforward biased toward the collectors 31 and 32 respectively. Diodes 29and 30 may be connected in series with and forward biased towardcollectors of the corresponding IGBTs 23 and 24 to provide them with thenecessary reverse blocking capability in AC applications. By external(on demand) on/off commands, synchronized drive signals of the gates 25and 26 may control the operation of the solid state bi-directionalswitch 12.

When the voltage across the switch 12 reaches the level of break downvoltage of the zener diodes 19 and 20, either the zener diode 19 orzener diode 20, depending on polarity of the voltage, may turn on in thevoltage-clamping mode. Consequently, one of the corresponding IGBT 23and 24 may be driven into an “active region” and may adjust (clamp) thevoltage across the switch 12 to that level. The diodes 30 and 29 mayblock forward biased current through the corresponding zener diodes 19and 20.

Referring to a schematic shown in FIG. 1B, in another embodiment, an ACSSSD 100 may include the switch 11 and a solid state bi-directionalswitch 112. The solid state bi-directional switch 112 may include firstand second RB-IGBTs 123 and 124 with gates 125, 126, emitters 127, 128,zener diodes 119 and 120, and diodes 121 and 122. The zener diode 119 inseries “back to back” with the diode 121 may be connected across thecollector 127 of the RB-IGBTs 124 and the gate 126 as a feedback circuitfor the RB-IGBTs 124 and, respectively, the zener diode 120 in series“back to back” with the diode 122 may be connected across the collector128 of the RB-IGBTs 123 and the gate 125 as a feedback circuit for theRB-IGBTs 123. The zener diodes 119 and 120 may be forward biased towardthe collectors 127 and 128 respectively. By external (on demand) on/offcommands, synchronized drive signals of gates 125 and 126 may controlthe operation of the solid state bi-directional switch 112.

Referring to FIG. 2, in yet another embodiment, a schematic conceptuallyrepresents a DC SSSD 200 having two types of solid state switches 211and 212 connected in parallel. There as well, for clearer illustrationof the main concept, the schematic omits gate resistors and a currentsensing mechanism well known in the art. The solid state switch 211 mayinclude a MOSFET 213 with a source 216 and a drain 217. Multiples ofMOSFET 231 may be added to the MOSFETs 213 for improved current carryingcapability and voltage drop. The solid state switch 212 may include IGBT223 with a gate 225, an emitter 227, and a zener diode 219 connectedacross the collector 217 of the IGBT 223 and the gate 225 and forwardbiased toward drain 217.

By external (on demand) on/off commands, a drive signal of the gate 215may control the operation of the solid state switch 211. When thevoltage across the switch 212 reaches a level of break down voltage ofzener diode 219, the zener diode 219 may turn on the solid state switch212 in the voltage clamping mode. Consequently, the IGBT 223 may bedriven into an “active region” and may adjust (clamp) the voltage acrossthe switch 212 to that level. Multiple MOSFETs 231 may act synchronouslywith the MOSFET 213 multiplying power carrying capability of the switch211. By external (on demand) on/off commands, the drive signal of thegate 225 may control the operation of the solid state switch 212.

The switching sequence of FIG. 3 depict an order of turning the SSSD 10of FIG. 1A, 100 of FIG. 1B, and 200 of FIG. 2 on and off in accordancewith the present invention, wherein graphs 301 and 302 represent theon/off state of MOSFET and IGBT respectively. Horizontal parts 311 and312 represent the “off” state, while horizontal parts 321 and 322characterize the “on” state in the graphs 301 and 302 respectively.Vertical parts 331 and 332 correspond to a turn on signal and verticalparts 341 and 342 signify a turn off signal in the graphs 301 and 302respectively.

Switching the power controlled by the SSSD 10 of FIG. 1A, 100 of FIG.1B, and 200 of FIG. 2 on requires an external command to generate thesignal 332 turning on the IGBT 23,24 of FIG. 1A, 123,124 of FIG. 1B, and223 of FIG. 2 first. After a delay T1 necessary for the dissipation ofinrush current of the IGBT, the signal 331 turns the MOSFET 13, 14 ofFIG. 1A and 213 of FIG. 2 on. Switching the power off requires anexternal command to generate the signal 341 turning the MOSFET off and,after a short delay T2 required for achieving the “off” state of theMOSFET, the signal 342 turns the IGBT off.

The SSSD of present invention would not generate current distortions,since when the voltage across the SSSD is below of “on” state voltagelevel of the IGBT in the switch 12 (112, 212), the switch 11 (211) mayautomatically take over the current conduction. For medium and highcurrent applications, low power dissipation (voltage drop) can beachieved by generally relying on the switch 11 (211) for normal currentconduction, and allowing the switch 12 (112, 212) to share the excessivecurrent in cases of fault. For higher current applications, the switch12 (112, 212) may share most of the conduction current during normalconduction without further increase of the power dissipation, as theon-state voltage of the IGBT would not change much with the draincurrent it conducts.

The flow chart of FIG. 4 depicts steps 400 of present invention. Anexternal signal 401 may cause a step 402 of connecting a power input toa power output through the IGBT. After delaying 403 for the dissipationof inrush current, step 404 of connecting the power input to the poweroutput through the MOSFET may follow that would bring the SSSD into anactive state. With the SSSD in the active state, an external signal 406may cause a step 405 of disconnecting the power input from said poweroutput through the MOSFET. After delaying 407 for switching off of theMOSFET, a step 408 of disconnecting the power input from the poweroutput through the IGBT may return the SSSD to the initial state.

The SSSD of present invention may improve reliability and fault currenthandling by relying on the switch 12 (112, 212) to handle switchingtransients and breaking up the fault current because a single IGBTtypically has much higher current rating than a single MOSFET of similarsize. The SSSD of the present invention may achieve higher currentratings in SSPC applications for lower than 1.7V voltage drop byconnecting in parallel additional MOSFETs with no limit of the faultcurrent handling capability of a single MOSFET. The switch 12 (112, 212)may provide over voltage protection for the SSSD during heavy inductiveload switching off, fault current breaking up transients, and lightningtransients.

It should be understood, of course, that the foregoing relates toexemplary embodiments of the invention and that modifications may bemade without departing from the spirit and scope of the invention as setforth in the following claims.

1. A method of switching a solid state switching device having at leastone metal oxide semiconductor field effect transistor and at least oneinsulated gate bipolar transistor connected in parallel comprising thesteps of: connecting on demand a power input to a power output throughsaid insulated gate bipolar transistor; delaying for the dissipation ofinrush current of said insulated gate bipolar transistor; connectingsaid power input to said power output through said metal oxidesemiconductor field effect transistor; disconnecting on demand saidpower input from said power output through metal oxide semiconductorfield effect transistor; delaying for switching off of said metal oxidesemiconductor field effect transistor; and disconnecting said powerinput from said power output through said insulated gate bipolartransistor.
 2. The method of claim 1, further comprising a step ofconnecting a feedback circuit between said power output and a gate ofsaid insulated gate bipolar transistor.
 3. The method of claim 2,further comprising a step of activating said feedback circuit when avoltage at said power output exceeds a predetermined level.
 4. Themethod of claim 3, wherein said feedback circuit alters a connection ofsaid power input to said power output through said insulated gatebipolar transistor for maintaining said voltage at said predeterminedlevel.
 5. A method of switching a solid state switching device having atleast one metal oxide semiconductor field effect transistor and at leastone insulated gate bipolar transistor connected in parallel comprisingthe steps of: connecting on demand a power input to a power outputthrough said insulated gate bipolar transistor; delaying for thedissipation of inrush current of said insulated gate bipolar transistor;connecting said power input to said power output through said metaloxide semiconductor field effect transistor; conveying negative feedbackfrom said power output to said insulated gate bipolar transistor;disconnecting on demand said power input to said power output throughsaid metal oxide semiconductor field effect transistor; delaying forswitching off of said metal oxide semiconductor field effect transistor;and disconnecting said power input from said power output through saidinsulated gate bipolar transistor.
 6. The method of claim 5, whereinsaid conveying of said negative feedback occurs when a voltage at saidpower output exceeds a predetermined level.
 7. The method of claim 6,wherein said conveying of said negative feedback alters said connectionof said power input to said power output through said insulated gatebipolar transistor for maintaining said voltage at said predeterminedlevel.
 8. A solid state switching device comprising: a first metal oxidesemiconductor field effect transistor; and a first insulated gatebipolar transistor connected in parallel with said metal oxidesemiconductor field effect transistor; a reverse biased zener diodeconnecting a collector and a gate of said first insulated gate bipolartransistor; wherein said first metal oxide semiconductor field effecttransistor turns on with a first predetermined delay after said firstinsulated gate bipolar transistor turns on and said first insulated gatebipolar transistor turns off with a second predetermined delay aftersaid first metal oxide semiconductor field effect transistor turns off.9. The solid state switching device of claim 8, further comprisingmultiple metal oxide semiconductor field effect transistors connected inparallel and turning on and off synchronously.
 10. The solid stateswitching device of claim 8, wherein said reverse biased zener diodehaving a predetermined breakdown voltage generates a negative feedbackfor maintaining an output voltage of said solid state switching deviceat a predetermined level.
 11. The solid state switching device of claim8, further comprising, for handling of AC current, a second metal oxidesemiconductor field effect transistor, a second insulated gate bipolartransistor, and first and second diodes, wherein said second metal oxidesemiconductor field effect transistor is connected in series and inopposite polarity with said first metal oxide semiconductor field effecttransistor, said second insulated gate bipolar transistor is connectedcounter-parallel with said first insulated gate bipolar transistor, saidfirst and second diodes are connected in series with said first andsecond insulated gate bipolar transistors correspondingly, said secondmetal oxide semiconductor field effect transistor turning on and offsynchronously with said first metal oxide semiconductor field effecttransistor, and said second insulated gate bipolar transistor turning onand off synchronous with said first insulated gate bipolar transistor.12. The solid state switching device of claim 11, wherein said first andsecond diodes are incorporated within said first and second insulatedgate bipolar transistors correspondingly.
 13. The solid state switchingdevice of claim 11, comprising multiple pairs of metal oxidesemiconductor field effect transistors connected in parallel with saidfirst and second metal oxide semiconductor field effect transistor andturning on and off synchronous with said first metal oxide semiconductorfield effect transistor.
 14. The solid state switching device of claim11, comprising a first link, containing a first reverse biased zenerdiode connected in series and in opposite polarity with a firstconventional diode, connecting a collector and a gate of said firstinsulated gate bipolar transistor and a second link, containing a secondreverse biased zener diode connected in series and in opposite polaritywith a second conventional diode, connecting a collector and a gate ofsaid second insulated gate bipolar transistor, wherein said gate of saidfirst metal oxide semiconductor field effect transistor is connected tosaid gate of said second metal oxide semiconductor field effecttransistor.
 15. The solid state switching device of claim 14, whereinsaid first and second reverse biased zener diodes have equalpredetermined breakdown voltages.
 16. The solid state switching deviceof claim 15, wherein said first and second reverse biased zener diodesgenerate a negative feedback for maintaining an output voltage of saidsolid state switching device at a predetermined level.